In a communication system, user equipment (UE), an evolved NodeB (eNodeB), and an access point (Access Point, AP) are included. The AP is a node including at least a radio frequency transceiver, and may be configured with a single antenna element or multiple antenna elements. One AP may be connected to one eNodeB. Multiple APs distributed in different locations may also be connected to one eNodeB. For example, in a coordinated multi-point transmitting/receiving (Coordinated Multi-Point, CoMP) system, multiple APs are connected to one eNodeB, which may coordinately transmit data and receive data from UE; these coordinating APs may be from the same eNodeB or from different eNodeBs. The UE may select an AP to access network and communicate with a peer end through the eNodeB.
Data transmission between the UE and the eNodeB in a hybrid automatic repeat request (HARQ) process is performed by using a user plane protocol stack. Referring to FIG. 1, the user plane protocol stack includes: a Packet Data Convergence Protocol (PDCP) layer, a radio link control (RLC) layer, a media access control (MAC) layer, and a physical layer (PHY). Taking that the UE sends data to the eNodeB as an example, specifically, the transmission is performed through the following manner: Data sent at a UE side is forwarded to the RLC layer after processed at the PDCP layer; the data processed by the RLC layer is forwarded to the MAC layer for processing, which continues until the highest layer in the user plane protocol stack at the UE side processes and sends the data to the eNodeB; at an eNodeB side, the PDCP layer receives and processes the data sent by the UE, which continues until the highest layer in the user plane protocol stack at the eNodeB side processes the received data and then sends a feedback message to the UE. Arrows in FIG. 1 indicate a path of the data transmission.
Generally, a cell (cell) may include one or multiple APs. When the UE moves between cells, the UE needs to select a cell to serve for the UE. In some systems, for example, a CoMP system, the UE selects multiple cells to serve for the UE. That is, the UE selects a cell as a serving cell (serving cell) to bear some control information (such as, scheduling information, PHY layer configuration parameters, and feedback information). Other cells providing only service information are called cooperating cells (cooperating cell). An eNodeB where the serving cell is located is a serving eNodeB (serving eNB) of the UE, and an eNodeB of other cooperating cells is a non-serving eNodeB (non-serving eNB).
When the UE moves between multiple cells, the UE is handed over between cells. In the prior art, during the UE is handed over between cells, a data forwarding channel is created between an eNodeB (hereinafter referred to as a source eNodeB) where a source serving cell of the UE is located and an eNodeB (hereinafter referred to as a target eNodeB) where a target serving cell of the UE is located. The source eNodeB sends data, for example, unnumbered data packet and correctly transmitted data in a service data unit (SDU) at the PDCP layer which are sent by the UE and received at the PDCP layer, to the target eNodeB, but the data transmission is not performed between the UE and the source eNodeB and between the UE and the target eNodeB; after the UE is handed over to a target cell, the data transmission is continued between the UE and the target eNodeB. In this way, in a handover process of the UE, a user plane is generally interrupted for 27.5 ms.
During the implementation and research of the present invention, the inventor of the present invention finds that message processing in the prior art has at least the following problem.
In the handover process, the source eNodeB sends unprocessed data received at the highest layer of the user plane protocol stack, that is, the PDCP layer, to the target eNodeB. In this way, a PDCP PDU section (RLC PDU) that has been correctly sent by the source eNodeB needs to reprocess the data at the target eNodeB.